1 OBJECTIVE Core B's primary responsibilities are to accrue a subject population; provide the clinical service for these subjects; maintain a cochlear implant patient registry; monitor postoperative residual hearing; and obtain audiologic outcome measures that will be used in the five research projects. Core B will also provide the technical and statistical support for all investigators. The five research projects are highly interdependent and interrelated. Each project depends on data generated by the others to address their specific aims, using similar patient populations to address the Clinical Research Center's overall goals. Described here are (1) extensive preoperative evaluations required for subject accrual; (2) specific populations to be studied; (3) cochlear implants to be used; (4) postoperative audiometric monitoring of residual hearing; (5) basic outcome measures of performance that will be obtained from subjects; and (6) the time-line of subject involvement. The overall statistical design, data management and technical support are also discussed. The individual projects describe the specific research questions and how each project is interactive and dependent on the others.